A motor is an important part in a fan. As systems to be cooled are becoming thinner and thinner, the thickness of a fan for use in this such of systems has to be reduced. Consequently, the thickness of the fan motor has to be reduce as well.
The bearing in a motor structure is an important part thereof. It can be understood to those skilled in the art that the bearing has to be pre-loaded so that it can operate in a good condition. There are some ways for pre-loading a bearing. For example, in U.S. Pat. No. 5,343,104, the bearing is pre-loaded by means of a projected portion of a bearing race and a thrust plate. A stopper is attached onto an end portion of a motor shaft against the thrust plate by means of press fitting. It is hard to make the fan disclosed in the '104 patent thinner because its fan motor includes many elements.
The structure of a conventional fan motor is now described here for explaining another way of pre-loading the bearing in the following. The structure as shown in FIG. 1 includes a housing 101, with a bearing seat 102 having a projected portion 102a located in the central portion of the housing. A bearing 103 and a bearing 104 are respectively inserted from above and from below into the bearing seat 102 and separated by the projected portion 102a. A shaft 105 is formed with a circumferential groove 105a and an impeller 108 is fixed on the shaft 105 for rotation therewith. Impeller 108 has a hub 108a and a plurality of blades 108b. A coil assembly 106 includes a silicon steel set 106a, an insulation portion 106b, a coil 106c, and a snap engaging portion 106d. A printed circuit board 107 is fixed on the housing 101 in a engagement with the snap engaging portion 106d; a spring 109, and a C-ring 110.
As shown in FIG. 1, the spring 109 is provided at the upper end of the bearing 104 and the C-ring 110 is provided at the lower end of the bearing 103 for pre-loading the bearings 103 and 104. The two ends of the spring 109 contact the bearing 104 and the hub 108a, respectively. The spring 109 and the projected portion 102a cooperatively pre-load the bearing 104. On the other hand, the C-ring 110 is engaged with the circumferential groove 105a. The elastic force provided by the spring 109 and the cooperation between the C-ring 110 and the projected portion 102a can fix and pre-load the bearing 103.
FIG. 2 is the free body diagram of the bearings 103 and 104 shown in FIG. 1. Referring to FIGS. 1 and 2, forces F1 and F2 are provided by the spring 109. Forces F3, F4, F5, and F6 are provided by the projected portion 102a. Forces F7 and F8 are provided by the C-ring 110. It can be understood that forces F1 to F4 pre-load the bearing 104 and forces F5 to F8 pre-load the bearing 103.
The drawbacks of the above conventional fan motor structure will be described in the following. As shown in FIG. 1, the bearing seat 102 is fixed in the housing 101 and the coil assembly 106 can be fixed to the outer surface of the bearing seat 102 by glue. The bearing seat 102, spring 109, and C-ring 110 cooperatively pre-load and fix the bearings 103 and 104. However, the vibrations generated when the motor operates is not absorbed if there is a tolerance between the bearing seat 102 and any of the bearings 103 and 104 because the bearing seat 102 and the bearings 103 and 104 are substantially rigid.
Moreover, the spring 109 and the C-ring 110 are primarily for pre-loading and fixing the bearings 103 and 104. If a single member can provide the same functions, then the manufacturing and assembling processes can be simplified and it becomes possible to provide a thinner motor.